354 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



largest fish obtained the reproductive organs are still func- 

 tional. The maximum size for the North Sea seems to be 

 28 inches, for the Danish seas it is smaller, about 22^ 

 inches. When the Iceland Plaice fisheries were first 

 exploited, very large specimens — over 30 inches in some 

 cases — were obtained. 



Migration and distribution.— Wherever the distribu- 

 tion in space of the Plaice has been attentively studied it 

 has been found that a very well marked segregation in 

 respect of the size of the fish exists. There is a close 

 correspondence between the size of the fish and the depth 

 of the water at the bottom of which it is found. The size 

 increases with the depth. The fish does not exist outside 

 the hundred fathom line, and indeed practically all the 

 fishing is carried on in seas varying from 20 to 50 fathoms 

 in depth. 



Since only the larger individuals are functionally 

 reproductive, it follows that the Plaice spawns only in 

 deep water, and it is the case that the spawning grounds 

 are always situated at some distance from the shore. 

 These spawning grounds are usually very definitely 

 located in any district. Thus on the East coast of Scot- 

 land such areas occur in the North about 16 miles seaward 

 from Moray Firth, and further South off St. Andrews Bay 

 and the Firth of Forth. In the Danish seas the fish only 

 spawns in the more open waters, such as in the eastern 

 parts of the Kattegat, in the Belts and in the Baltic. In 

 the Irish Sea the positions of some such spawning grounds 

 have also been determined, and one notable area lies East 

 from the South end of the Isle of Man in a depression 

 having an average depth of about 23 fathoms and sur- 

 rounded by water of 16-20 fathoms in depth. The bottom 

 consists of soft bluish-black mud with an abundant fauna. 

 Scrobicularia and Turritella are very abundant, and the 



